The tight confines of oil well casings limit the space in which to run production tubing strings having submersible pump arrangements at their bottom ends for pumping oil and other fluids through great depths to the surface. In a production casing of 5.5 inches (aprox. 139.7 mm) diameter, the available space for a pump arrangement is about 4.85 inches (123.2 mm). Small electric submersible or subsurface pump drives have been used with progressive cavity pumps for these purposes. Subsurface drives are particularly suited for use in deviated and horizontal wells since they do not employ a turning drive shaft which extends from the well's surface; and, progressive cavity pumps are preferred since they can pump liquids containing sand and other particular matter which is often mixed with production fluids. Although the electric submersible pumps fit within the tight confines of a well casing, they suffer from several drawbacks in oil well applications: they are not good for pumping fluids mixed with solids; they require a permanent electrical service; they are expensive to install; and they frequently suffer from pinched power lines since electric cable is attached to the exterior of the production tubing.
It would be preferable to replace the electric submersible pumps with much less expensive hydraulic submersible pump drives or motors which are typically used in other oil field applications, such as current surface drives, mobile tank trucks, service rigs, and hydraulic reciprocating pumping units. Such drive motors are attractive since fewer specialty components are required for installation and operation. However, these motors are fairly bulky and tend to restrict production fluid flow through a pump arrangement. In particular, a problem exists with the mounting assemblies which must be employed about the drive motors for centralizing and supporting the drive motors within the pump assemblies. Unfortunately, the area about the drive motors forms a "bottle neck" for the produced fluids since the flow area is the most constricted in this location. Therefore, the mounting assemblies exacerbate the problem by further restricting the already limited fluid flow area. Even the physically smaller electric drives are mounted below progressive cavity pumps to avoid undue restriction and fluid flow past the electric motor in the production tubing above the pump.
Another problem with current pump drives , both electric and hydraulic ones, is that the production fluid flowing to or past the drive assembly pump directly impacts the upstream bearing pack which houses the pump's drive shaft. Such fluid impact (and the suspended particulate matter) deteriorates the bearing pack seals and causes leaks into the bearings over a relatively short operational time span. For conventional surface drives such seals can be readily serviced to avoid surface oil spills. In subsurface drives, however, the drive pump equipment cannot be serviced until a failure occurs and must be retrieved for servicing and replacement. Therefore protecting and extending the operating life of these seals will prevent frequent and costly servicing.
What is therefore desired is a novel submersible pump arrangement for use with oil well production tubing which overcomes the limitations and disadvantages of the existing arrangements. Preferably, it should allow the use of hydraulic drive motors in such pump arrangements for pumping production fluids. In particular, it should provide a flow control assembly for supporting a hydraulic drive motor within the pump arrangement without restricting the fluid flow area about the drive motor body. The flow control assembly should further reduce the impact of fluid flow on the bearing pack of the drive motor to increase the operational life of its seals and bearings, and thus reduce servicing costs.